If you work on raw files, RT doesn't modify the file itself, it only shows the area which will be cropped. When you reopen the file, the crop area will be displayed again because the raw file is not modified. When you export to jpg or TIFF or PNG, the output file will be cropped. The advantage of this is that you would always be able to adjust the crop area by simply dragging the borders. I think most raw converter act this way, at least it's not something never seen before.

Photoshop Elements 9 does!Mostly I crop stuff out because it looks distracting, so to still see it, is distracting.I'm sure it can be done easily without saving to file (which I don't want), given that you keep a complete history of what has happened since the crop.

No, with the 9-key you control what you see after cropping.
The topmost setting uses the transparency mask from the gui settings, the middle settings adds a black frame, the bottom setting uses a white frame. And this setting works immediately.
The left button shows the original size maximized and the right button shows the cropped area maximized.

When you work on a raw file the original file is not changed and the sidecar file is used on reloading to reapply the changes. If you work on a non-raw file like a jpeg, the cropping is indeed applied to the file on save and you are no longer able to revert to the original settings.